More than 300 hectares of forest in southern Vietnam were reduced to ashes in a blaze that has been burning for five days, shrinking the habitat of the rare red-headed crane.

The fire started inTramChim National Park's Zone A1at around 9 a.m. on Sunday and then spread to the neighboring Zone A2 at 11 a.m. on Monday.

It is stilling raging in the two zones, authorities of the park, located in the Mekong Delta province of Dong Thap, said on Thursday.

The park's management board mobilized more than 550 people, including firefighters, police, and residents to douse the flames.

But they struggled to make progress as fire engines could not access the scene due to complicated canal-ridden topography.

"We had to use 40-50 water pipes to send water a full kilometer from canals to the fire," said Huynh Van Dap, a head of the local fire squad.

"The flames just keep burning. As soon as one fire is stamped out, another breaks out, and so on. We are exhausted," he said.

Park authorities said the fire had burnt more than 300 hectares, including 170 hectares of spikerushes that the rare red-headed cranes had once made their home. Spikerushes are the cranes' favorite food.

The fire has also destroyed 50 ha of cajput forests, said park rangers.

"Cigarette butts residents threw on the ground might have triggered the fire. They illegally came to the park to catch fish," he said.

The 7,300-hectare Tram Chim National Park includes nearly 3,000 hectares of cajuput forest which is considered the "lung" of the Dong Thap Muoi region.

With a system of swamps, grass-plots and criss-crossing canals, the park is also a habitat for more than 300 species of plants, 130 species of fresh-water fish and 231 species of birds such as pelicans, storks, herons, spot-billed ducks, water chickens and red-headed cranes.

The fire itself may panic red-headed cranes while the burnt spikerushes field in Zone A1 means their habitats in Tram Chim National Park have shrunk, environmentalists said, adding many of the cranes might have flown away.

Around 85 of the birds had been spotted in the park, mostly in Zone A1 and A5, before the fire, according to park authorities.

Red-headed crane, known as hac by Vietnamese people, is listed in the World's Red Book of Threatened Species.

It is one of 15 species of cranes worldwide and is found mainly in India and Southeast Asia. It is the tallest, standing at six feet tall, has a wingspan of eight feet.